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|
package driver
import (
"fmt"
"io"
"io/ioutil"
"github.com/nihei9/maleeni/compiler"
)
type Token struct {
ID int
Match []byte
EOF bool
Invalid bool
}
func newToken(id int, match []byte) *Token {
return &Token{
ID: id,
Match: match,
}
}
func newEOFToken() *Token {
return &Token{
ID: 0,
EOF: true,
}
}
func newInvalidToken(match []byte) *Token {
return &Token{
ID: 0,
Match: match,
Invalid: true,
}
}
type lexer struct {
tranTab *compiler.TransitionTable
src []byte
srcPtr int
tokBuf []*Token
}
func NewLexer(tranTab *compiler.TransitionTable, src io.Reader) (*lexer, error) {
b, err := ioutil.ReadAll(src)
if err != nil {
return nil, err
}
return &lexer{
tranTab: tranTab,
src: b,
srcPtr: 0,
}, nil
}
func (l *lexer) Next() (*Token, error) {
if len(l.tokBuf) > 0 {
tok := l.tokBuf[0]
l.tokBuf = l.tokBuf[1:]
return tok, nil
}
tok, err := l.next()
if err != nil {
return nil, err
}
if !tok.Invalid {
return tok, nil
}
errTok := tok
for {
tok, err = l.next()
if err != nil {
return nil, err
}
if !tok.Invalid {
break
}
errTok.Match = append(errTok.Match, tok.Match...)
}
l.tokBuf = append(l.tokBuf, tok)
return errTok, nil
}
func (l *lexer) Peek1() (*Token, error) {
return l.peekN(0)
}
func (l *lexer) Peek2() (*Token, error) {
return l.peekN(1)
}
func (l *lexer) Peek3() (*Token, error) {
return l.peekN(2)
}
func (l *lexer) peekN(n int) (*Token, error) {
if n < 0 || n > 2 {
return nil, fmt.Errorf("peekN() can handle only [0..2]")
}
for len(l.tokBuf) < n+1 {
tok, err := l.next()
if err != nil {
return nil, err
}
l.tokBuf = append(l.tokBuf, tok)
}
return l.tokBuf[n], nil
}
func (l *lexer) next() (*Token, error) {
state := l.tranTab.InitialState
buf := []byte{}
unfixedBufLen := 0
var tok *Token
for {
v, eof := l.read()
if eof {
if tok != nil {
l.unread(unfixedBufLen)
return tok, nil
}
return newEOFToken(), nil
}
buf = append(buf, v)
unfixedBufLen++
entry := l.tranTab.Transition[state]
if len(entry) == 0 {
return nil, fmt.Errorf("no transition entry; state: %v", state)
}
nextState := entry[v]
if nextState == 0 {
if tok != nil {
l.unread(unfixedBufLen)
return tok, nil
}
return newInvalidToken(buf), nil
}
state = nextState
id, ok := l.tranTab.AcceptingStates[state]
if ok {
tok = newToken(id, buf)
unfixedBufLen = 0
}
}
}
func (l *lexer) read() (byte, bool) {
if l.srcPtr >= len(l.src) {
return 0, true
}
b := l.src[l.srcPtr]
l.srcPtr++
return b, false
}
func (l *lexer) unread(n int) {
l.srcPtr -= n
}
|
